## Lattice congruences, fans and Hopf algebras

Venue: | J. Combin. Theory Ser. A |

Citations: | 17 - 8 self |

### BibTeX

@ARTICLE{Reading_latticecongruences,,

author = {Nathan Reading},

title = {Lattice congruences, fans and Hopf algebras},

journal = {J. Combin. Theory Ser. A},

year = {},

pages = {237--273}

}

### OpenURL

### Abstract

Abstract. We give a unified explanation of the geometric and algebraic properties of two well-known maps, one from permutations to triangulations, and another from permutations to subsets. Furthermore we give a broad generalization of the maps. Specifically, for any lattice congruence of the weak order on a Coxeter group we construct a complete fan of convex cones with strong properties relative to the corresponding lattice quotient of the weak order. We show that if a family of lattice congruences on the symmetric groups satisfies certain compatibility conditions then the family defines a sub Hopf algebra of the Malvenuto-Reutenauer Hopf algebra of permutations. Such a sub Hopf algebra has a basis which is described by a type of pattern-avoidance. Applying these results, we build the Malvenuto-Reutenauer algebra as the limit of an infinite sequence of smaller algebras, where the second algebra in the sequence is the Hopf algebra of non-commutative symmetric functions. We also associate both a fan and a Hopf algebra to a set of permutations which appears to be equinumerous with the Baxter permutations. 1.